Method for improving flavor of sesame oil through germination pretreatment

Abstract

The invention discloses a method for improving the flavor of sesame oil by utilizing germination pretreatment. The method specifically comprises the following steps: step 1, cleaning raw materials; step 2, soaking the sesame seeds in water for 1-4 hours until the water content is 30-45%; step 3, uniformly placing the imbibed sesame seeds in a tray, placing the tray in a constant-temperature and constant-humidity incubator, setting the temperature to be 25-30 DEG C, setting the relative humidity to be 60-100%, and cultivating for 2-24 hours, wherein the spreading thickness of the sesame seeds is less than or equal to 1 cm; step 4, drying the sesames: drying the sesames subjected to germination treatment until the moisture content is 5-15%; step five, baking the sesame to produce fragrance; and 6, extracting oil by adopting a physical squeezing or stone milling water extraction method, and filtering to remove impurities to obtain the sesame oil. On the basis of not changing the existing sesame oil production process, compared with the sesame oil prepared by the traditional process, the prepared sesame oil is fuller in flavor and richer in fragrance, and meanwhile, a relatively high oil yield is still kept.

Description

Technical Field

[0001] The invention belongs to the technical field of sesame oil processing and flavor enhancement, and particularly relates to a method for improving the flavor of sesame oil by utilizing germination pretreatment. Background Art

[0002] Sesame oil is a very popular seasoning oil for consumers. It is often used in hot pots, cold dishes, etc. to increase the flavor of food. Sesame oil with a strong flavor can bring good sensory enjoyment to consumers and has high market competitiveness. Therefore, sesame oil processing companies have long been committed to continuously improving the flavor quality of sesame oil.

[0003] Sesame oil is a typical heat-processed flavor food, and its rich aroma comes from the high-temperature seed frying process. The flavor precursors in sesame seeds mainly include fatty acids, oligosaccharides, monosaccharides, amino acids, oligopeptides, etc. The precursors themselves do not have flavor activity, but after thermal reaction, they can form characteristic aroma components of sesame oil such as heterocyclics, phenols, aldehydes, ketones, etc. In the traditional high-temperature seed roasting aroma production process, the proportion of precursors that actually participate in the thermal reaction to form the characteristic flavor of sesame oil is very low, mainly including a limited amount of free oligosaccharides, amino acids, oligopeptides and fatty acids that exist naturally in the oil. The large molecular polysaccharides and proteins rich in sesame can also release some small molecular aroma precursors after thermal cracking, but the efficiency of this thermal cracking to release flavor precursors is extremely low. Most of the structural polysaccharides, proteins and oils are not fully thermally cracked in the high-temperature seed frying process and do not participate in the formation of sesame oil flavor.

[0004] Adding exogenous enzymes (saccharifying enzymes, proteases, etc.) to sesame meal can efficiently degrade macromolecular proteins and polysaccharides in sesame meal under mild conditions, release more small molecular flavor precursors, and then mix with refined sesame oil and heat to produce fragrance to obtain strong-flavored sesame oil (Chinese patents CN201510793227.0, CN202210991327.4, CN202211126400.8). However, this type of exogenous enzyme flavoring method does not meet the national standard that sesame oil and small-milled sesame oil must be prepared from sesame seeds by pressing or water substitution. Exogenous enzymes are expensive, and the enzymatic hydrolysis process involves seed crushing, the addition of enzymatic hydrolyzate and the removal of water, which cannot be directly applied to existing process equipment and production lines. These factors greatly limit the application and promotion of exogenous enzymes in sesame oil processing and production. In addition, the flavor characteristics of sesame oil prepared by exogenous enzyme enzymatic hydrolysis-thermal reaction are quite different from those of sesame oil prepared by traditional methods. Consumers are not familiar with its flavor characteristics, which affects its market acceptance.

[0005] The endogenous enzymes naturally present in sesame seeds are activated during the germination process. Existing studies have found that after germination treatment, the polysaccharide, protein and oil content of sesame seeds is reduced, the tocopherol and sesamol content is increased, the nutritional value and oxidative stability of sesame oil are increased, and the physical and chemical properties such as acid value, peroxide value, and fatty acid composition are in line with national standards (Chinese patents CN202010730581.X, CN201210324157.0). However, germination pretreatment of sesame raw materials as a potential technical means to improve the flavor quality of sesame oil has not yet been studied and developed.

[0006] It is necessary to develop a new flavoring method that does not require large-scale changes to the existing sesame oil and small-milled sesame oil production processes and equipment, and can significantly improve the characteristic flavor of sesame oil. Compared with the flavoring effect of exogenous enzymes, the application of sesame's natural endogenous enzymes in sesame oil flavoring is more economical and feasible, can be combined with existing processes, and is suitable for rapid promotion and application in sesame oil companies. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention utilizes a sesame germination pretreatment technology under specific conditions to promote the release of flavor precursors in sesame by increasing the activity of endogenous enzymes in sesame, and then stir-fries the germinated sesame seeds and subject them to physical pressing or stone-milling water replacement technology to produce sesame oil or small-milled sesame oil with better flavor quality and richer aroma, while ensuring a higher oil extraction rate, and having good prospects for industrial application.

[0008] The present invention is a method for improving the flavor of sesame oil by using germination pretreatment, which uses germination pretreatment of sesame raw materials under specific conditions to improve the activity of endogenous enzymes in sesame, effectively promotes the enzymatic release of small molecular flavor precursors in sesame, and prepares sesame oil or small-milled sesame oil with better flavor quality and richer aroma by frying germination sesame seeds at high temperature and then physically pressing or stone-milling water-replacement process. The specific steps are as follows:

[0009] (1) Step 1: Raw material cleaning: Select fresh sesame seeds that are full, undamaged, free of pests and diseases as raw materials, and remove impurities and immature or spoiled sesame seeds from the raw materials;

[0010] (2) Step 2: Soaking and swelling sesame seeds: After washing the sesame seeds with purified water, soak the sesame seeds in water for 1-4 hours, so that the sesame seeds swell to a moisture content of 30-45%;

[0011] (3) Step 3: Specific conditions for sesame germination pretreatment: Place the swelled sesame seeds evenly on a tray, with a sesame layer thickness of ≤1 cm, and place the tray in a constant temperature and humidity incubator with a temperature set at 25-30°C and a relative humidity set at 60-100% for 2-24 hours;

[0012] (4) Step 4, drying the sprouted sesame seeds: placing the sprouted sesame seeds in an oven and drying them at 25-50° C., or freeze drying the sprouted sesame seeds at ≤-50° C.;

[0013] (5) Step 5, sesame roasting: put the sesame seeds into a hot air seed roasting machine, roast at 140-220° C. for 20-60 min, or place the sesame seeds in a microwave at a power of 540-900 W for 5-15 min, and cool to room temperature after roasting;

[0014] (6) Step 6, oil extraction: physical pressing or stone mill water replacement method is used to extract oil. ① Physical pressing method: Use a screw press or hydraulic press to physically press the roasted and cooled sesame seeds, centrifuge or sedimentation filter to remove impurities, and obtain sesame oil. ② Stone mill water replacement method: The roasted sesame seeds are stirred with water, stone milled, oiled, skimmed, filtered, etc. to obtain small-milled sesame oil.

[0015] (7) Sesame seeds can be germinated in the absence of light or in the presence of light.

[0016] (8) Preferably, the amount of pure water added for soaking sesame is water (mL): sesame (g) ≥ 1.5: 1. (9) Preferably, in order to improve the flavor of sesame oil, avoid a significant increase in the acid value of sesame oil, and ensure a high oil extraction rate, the optimal conditions for germination are 25°C, relative humidity ≥ 90%, and germination for 18 hours without light. Under this germination condition, the flavor quality of sesame oil is the best.

[0017] (10) Preferably, the sprouted sesame seeds are dried to a suitable moisture content of 5-15% before roasting, which is conducive to the preparation of sesame oil with a strong and harmonious flavor.

[0018] Compared with the prior art, the present invention uses a germination pretreatment technology under specific conditions to improve the activity of endogenous enzymes in sesame, promote the release of flavor precursors in sesame, and improve the formation of aroma when sesame seeds are fried. The sesame oil and small-milled sesame oil prepared by the method have better flavor quality, fuller flavor, and richer aroma than traditional sesame oil, while still maintaining a high oil yield. The method for enhancing the flavor of sesame oil and small-milled sesame oil provided by the present invention is simple and safe, does not require the addition of additional raw materials other than sesame, meets national standards, and has better flavor enhancement effect and economic cost than existing exogenous enzyme methods, and has good prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a process flow chart of the present invention;

[0020] Figure 2 The sensory profile of sesame oil prepared in each embodiment;

[0021] Figure 3 is a heat map of the volatile matter content of sesame oil prepared in each example;

[0022] Figure 4 The activity changes of endogenous enzymes in sesame during germination, including (a) α-amylase, (b) lipase, (c) acid protease, and (d) neutral protease;

[0023] Figure 5 The difference in the content of flavor precursors in each example, (a) soluble sugar, (b) free amino acids. DETAILED DESCRIPTION

[0024] The present invention is described in more detail below in conjunction with specific embodiments. The specific parameters in the embodiments are only used to illustrate the present invention and are not used to limit the scope. Those skilled in the art can appropriately modify the parameters of the present invention.

[0025] Example 1

[0026] Take 300g of sesame seeds and wash them three times with pure water, then add 500mL of pure water and soak them at room temperature (25℃) for 2h, and drain the water. Spread the swollen sesame seeds evenly on a tray (32.5cm×24.5cm×4.5cm), place the tray in an incubator, and cultivate for 6h at 25℃, 90% relative humidity, and no light. Dry the sprouted sesame seeds in a 25℃ oven to a moisture content of 6.5%. Put the dried sesame seeds into a hot air seed roasting machine, roast at 200℃ for 20min, and cool to room temperature. Use a screw press to squeeze the sesame seeds to obtain sesame oil, centrifuge at 4000rpm for 10min to remove impurities, and obtain clarified sesame oil.

[0027] Example 2

[0028] Take 300g of sesame seeds and wash them three times with pure water, then add 500mL of pure water and soak them at room temperature (25℃) for 2h, and drain the water. Spread the swollen sesame seeds evenly on a tray (32.5cm×24.5cm×4.5cm), place the tray in an incubator, and cultivate for 12h at 25℃, 90% relative humidity, and no light. Dry the sprouted sesame seeds in a 25℃ oven to a moisture content of 6.5%. Put the dried sesame seeds into a hot air seed roaster, roast at 200℃ for 20min, and cool to room temperature. Use a screw press to squeeze the sesame seeds to obtain sesame oil, centrifuge at 4000rpm for 10min to remove impurities, and obtain clarified sesame oil.

[0029] Example 3

[0030] Take 300g of sesame seeds and wash them three times with pure water, then add 500mL of pure water and soak them at room temperature (25℃) for 2h, and drain the water. Spread the swollen sesame seeds evenly on a tray (32.5cm×24.5cm×4.5cm), place the tray in an incubator, and cultivate for 18h at 25℃, 90% relative humidity, and no light. Dry the sprouted sesame seeds in a 25℃ oven to a moisture content of 6.5%. Put the dried sesame seeds into a hot air seed roaster, roast at 200℃ for 20min, and cool to room temperature. Use a screw press to squeeze the sesame seeds to obtain sesame oil, centrifuge at 4000rpm for 10min to remove impurities, and obtain clarified sesame oil.

[0031] Example 4

[0032] Take 300g of sesame seeds and wash them three times with pure water, then add 500mL of pure water and soak them at room temperature (25℃) for 2h, and drain the water. Spread the swollen sesame seeds evenly on a tray (32.5cm×24.5cm×4.5cm), place the tray in an incubator, and cultivate it for 24h at 25℃, 90% relative humidity, and no light. Dry the sprouted sesame seeds in a 25℃ oven to a moisture content of 6.5%. Put the dried sesame seeds into a hot air seed roasting machine, roast them at 200℃ for 20min, and cool them to room temperature. Use a screw press to squeeze the sesame seeds to obtain sesame oil, centrifuge at 4000rpm for 10min to remove impurities, and obtain clarified sesame oil.

[0033] Comparative Example 1

[0034] Take 300g of sesame seeds and wash them three times with pure water, then add 500mL of pure water and soak them at room temperature (25℃) for 2h, and drain the water. After swelling, the sesame seeds are directly dried in a 25℃ oven to a moisture content of 6.5% without germination culture. The dried sesame seeds are placed in a hot air seed roasting machine, roasted at 200℃ for 20min, and cooled to room temperature. Sesame seeds are squeezed with a screw press to obtain sesame oil, and centrifuged at 4000rpm for 10min to remove impurities to obtain clarified sesame oil.

[0035] Comparative Example 2

[0036] 10g defatted sesame meal was mixed with 100mL deionized water, and 12U / mg cellulase was added to hydrolyze at pH 4.8 and 50℃ for 2h; 180U / mg xylanase was added to hydrolyze at pH 5.0 and 50℃ for 2h; then 10U / mg alkaline protease was added to hydrolyze at pH 9.5 and 50℃ for 2h; 0.8U / mg flavor protease was added to hydrolyze at pH 7.5 and 50℃ for 2h. The enzymatic solution was adjusted to neutral and heated at 90℃ for 10min to inactivate the enzyme, centrifuged at 5000r / min for 5min, and the supernatant enzymatic solution was freeze-dried (-65℃, 5Pa, 12h). The sesame meal enzyme thaw was dissolved in 0.2mol / L, pH 6.5 phosphate buffer (5:1, mL:g), and cold-pressed sesame oil (3:1, mL:g) was added, and the reaction was heated at 140℃ and 800rpm for 1h to obtain the flavor base. After the flavor base is cooled, it is mixed with cold-pressed sesame oil in a ratio of 1:6 (w:w) for extraction, stirred at 25°C for 6 hours, and dehydrated with anhydrous sodium sulfate. The precipitate is removed by centrifugation at 5000 rpm for 10 minutes to obtain the upper layer of rich-flavor sesame oil.

[0037] Comparative Example 3

[0038] Take 300g of sesame seeds and wash them three times with pure water, then add 500mL of pure water and soak them at room temperature (25℃) for 2h, and drain the water. Spread the swollen sesame seeds evenly on a tray (32.5cm×24.5cm×4.5cm), place the tray in an incubator, and cultivate for 30h at 25℃, 90% relative humidity, and no light. Dry the sprouted sesame seeds in a 25℃ oven to a moisture content of 6.5%. Put the dried sesame seeds into a hot air seed roaster, roast at 200℃ for 20min, and cool to room temperature. Use a screw press to squeeze the sesame seeds to obtain sesame oil, centrifuge at 4000rpm for 10min to remove impurities, and obtain clarified sesame oil.

[0039] Compared with the sesame oil without sprouting pretreatment (Comparative Example 1), the sesame oil prepared after 6-18h sprouting at 25°C (Examples 1, 2, 3, 4) has better flavor, richer aroma, and more harmonious overall flavor, showing richer fresh flavor, nut flavor, caramel flavor, roasted sesame flavor, caramel flavor and butter flavor ( Figure 2 ), while the concentrations of pyrazines, pyridines, pyrroles, phenols, and sulfur-containing volatile flavor compounds in sesame oil increased ( Figure 3). When the germination time is increased to 24h (Example 4), the smoky flavor of sesame oil (Example 4) is significantly enhanced due to the significant increase in phenolic substances (smoky flavor characteristics). The smoky flavor sensoryly suppresses the characteristic flavors of sesame oil such as fresh flavor, nutty flavor, burnt flavor, roasted sesame flavor, caramel flavor and buttery flavor. Therefore, the overall flavor quality of Example 4 is lower than that of Example 3 (18h germination). When the germination pretreatment time is further increased to 30h (Comparative Example 3), due to the strong smoky flavor of sesame oil, the inhibitory effect on fresh flavor, nutty flavor, burnt flavor, roasted sesame flavor, caramel flavor and buttery flavor is prominent, resulting in a reduction in the intensity of the characteristic flavor of sesame oil and an imbalance and disharmony of the overall aroma ( Figure 2 ), indicating that germination for 30 h cannot improve the flavor quality of sesame oil. In addition, germination for 30 h caused a significant loss in the oil content (crude fat) of sesame (>4%, Table 1).

[0040] The above results show that the germination pretreatment under the specific conditions of the present invention (e.g., temperature 25°C, time 6-24h) has the effect of improving the overall flavor quality of sesame oil, which is manifested as a richer and more harmonious aroma, while ensuring a higher oil yield (oil loss rate <3%) (Table 1).

[0041] As the germination pretreatment time increases, the activities of endogenous enzymes in sesame, including α-amylase, lipase, and protease, gradually increase ( Figure 4 ), while the content of macromolecular substances in sesame, including protein, oil and polysaccharide, gradually decreased (Table 1), and more soluble sugars and free amino acids were formed by degradation ( Figure 5 ) and other small molecule flavor precursor substances. The present invention utilizes germination pretreatment under specific conditions to increase the activity of endogenous enzymes in sesame, promotes the enzymatic release of small molecule flavor precursor substances in sesame, and achieves the improvement of sesame oil flavor quality.

[0042] Compared with the traditional sesame oil (Comparative Example 1), the sensory intensity of butter flavor, caramel flavor and nut flavor of sesame oil (Comparative Example 2) prepared by enzymatic hydrolysis of sesame meal with exogenous enzymes was significantly enhanced, but the caramel flavor, roasted sesame flavor, fresh flavor, etc. were not significantly improved or even decreased ( Figure 2 ). The strong and prominent butter and caramel flavors exhibited by Comparative Example 2 are quite different from the flavor profile of traditional sesame oil, which reduces consumers' familiarity and acceptance of the product.

[0043] The method for improving the flavor of sesame oil by using germination pretreatment under specific conditions of the present invention has a better flavor enhancement effect than the exogenous enzyme method, showing a more natural and harmonious overall aroma profile. The method for enhancing the flavor of sesame oil of the present invention has simple process operation, good repeatability, and is easy to realize industrial production, and can meet a wide range of market needs.

[0044] Table 1 Differences in crude fat, crude protein and total sugar content of sesame (g / 100g)

[0045]

Claims

1. A method for improving the flavor of sesame oil by using germination pretreatment, characterized in that: The method comprises the following steps: (1) Step 1: Raw material cleaning: remove impurities and immature and spoiled sesame seeds from the raw sesame; (2) Step 2: Soaking and swelling sesame seeds: After washing the sesame seeds with pure water, soak the sesame seeds in water for 1-4 hours, so that the sesame seeds swell to a moisture content of 30-45%; (3) Step 3, sesame germination pretreatment: Place the sesame seeds evenly on a tray after swelling, with the thickness of the sesame seeds ≤ 1 cm, and place the tray in a constant temperature and humidity incubator with the temperature set to 25-30°C and the relative humidity set to 60-100% for 2-24 h; (4) Step 4: Drying the sprouted sesame seeds: Dry the sprouted sesame seeds to a moisture content of 5-15%; (5) Step 5: Roasting sesame seeds: roasting sesame seeds to produce fragrance; (6) Step 6: Extracting oil: Extracting oil by physical pressing or stone mill water substitution method, filtering and removing impurities to obtain sesame oil.

2. The method according to claim 1, characterized in that: The weight ratio of the purified water and sesame added in step 2 is water: sesame ≥ 1.5:

1.

3. The method according to claim 1, characterized in that: In step three, the germination conditions of sesame are 25°C, humidity ≥ 90%, and germination for 18 hours without light.

4. The method according to claim 1, characterized in that: The drying method in step 4 is to place the sprouted sesame seeds in an oven for heat drying at 25-50° C., or to freeze-dry the sprouted sesame seeds at ≤-50° C.

5. The method according to claim 1, characterized in that: The sesame roasting conditions in step five are as follows: placing the sesame seeds in a hot air seed roasting machine and roasting them at 140-220° C. for 20-60 min, or placing the sesame seeds in a microwave at a power of 540-900 W for 5-15 min, and cooling them to room temperature after roasting.

6. The method according to claim 1, characterized in that: Step six: physical pressing is used to extract oil. The roasted and cooled sesame seeds are physically pressed with a screw press or a hydraulic press, and then centrifuged or filtered by sedimentation to remove impurities, thereby obtaining sesame oil.

7. The method according to claim 1, characterized in that: Step six is ​​to extract oil by stone-grinding water method, in which the roasted sesame seeds are mixed with water, ground with stone, pounded and shaken, skimmed and filtered to obtain small-ground sesame oil.

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